Optical techniques such as single wavelength transmission, differential absorption, laser-induced fluorescence and stimulated Raman scattering are typically used to provide quantitative measurements of soil, water and air contaminants. In recent years, the ability of these optical techniques to provide remote measurements has been facilitated by using optical fibers coupled to lasers operating at wavelengths selected to provide high measurement sensitivity. For many applications, the optimum wavelengths for high measurement sensitivity lie in the UV to visible region of the spectrum. Unfortunately, because of excessive attenuation, it is difficult to propagate the optimal measurement wavelengths very far in commercially available optical fibers. This limitation has restricted remote fiber-based sensor systems to either short ranges, i.e., a few meters, when operating at UV wavelengths or to long ranges at non-optimal measurement wavelengths.
A need exists, therefore, for a remote fiber-based sensor system that can efficiently operate over long distances while retaining the high measurement sensitivity of UV light.